고강도 콘크리트를 사용한 철근콘크리트 보 처짐의 불확실성 분석

최봉섭(Choi Bong-Seob) 대한건축학회 2006 大韓建築學會論文集 : 構造系 Vol.22 No.1

층상 유한요소를 이용한 철근콘크리트 보의 처짐 해석 모델

최봉섭(Choi,, Bong-Seob),권영웅(Kwon, Young-Wung) 한국콘크리트학회 1999 콘크리트학회논문집 Vol.11 No.5

아동의 만들기 체험활동을 위한 TSM 통합교육 프로그램 개발

최봉섭(Choi Bong Seob),이시원(Lee Si Won) 한국실과교육학회 2004 한국실과교육학회지 Vol.17 No.3

The purpose of the study was to develop TSM integration education program for making a model boat, hands-on activity. The theme was chosen because 5 and 6th graders had been highly perceived and interested in. Basically, the study was performed following three steps. 1. Preparation step : analyzing the 7th curriculum Practical Arts, Science and Mathematics associated with making a model boat, organizing theme-web, selecting and organizing the integration program contents, setting the objectives and planning theme learning. 2. Development step : developing design brief, student’s activity and teacher’s guide. 3. Improvement step : establishing the validity and the reliability of the TSM program through questionnaires of experts and students. The program, result of the study was consisted of 5 sub-themes including. 1) keeping balance, 2) taking a step forward, 3) changing the direction, 4) operating a circuit tester, 5) making a model boat. It is expected that the TSM integration program will develop the problem-solving ability, the curiosity and interest about Practical Arts, Science and Mathematics. Lastly this program can be applied flexibly to discretionary activities, extra curriculums, experiential activities and regular activities. Many kinds of TSM integration program have to be developed in order to satisfy various children’s demands and improve efficiency in experiential education.

장기하중이 FRP-보강근 콘크리트 보의 휨균열폭에 미치는 영향

최봉섭(Bong-Seob Choi) 한국산학기술학회 2018 한국산학기술학회논문지 Vol.19 No.12

FRP-보강근 콘크리트 부재들은 FRP-보강근이 철근에 비해 낮은 탄성계수와 부착강도를 갖고 있어 철근콘크리트 부재에 비해 과도한 균열폭의 가능성이 클 수 있다. 따라서 외국의 기준들에서는 FRP-보강근 콘크리트 부재의 균열제어를 위하여 허용균열폭의 제한규정을 두고 있는데, ACI 440.1R-15 설계지침에서는 최대 보강근 간격으로 제어하는 간접적인 방법으로 제안하고 있다. 그러나 제안식은 아직까지 장기하중이 균열폭에 미치는 시간종속적인 효과를 반영하지 못하고 있다. 이에 본 연구에서는 장방형단면뿐만 아니라 T형단면의 FRP-보강근 콘크리트 보를 대상으로 장기실험을 통하여 얻어진 실험결과를 바탕으로 단면형태별 균열폭 특성을 구분하여 파악하므로 써 장기균열폭 예측모델을 제안하는데 필요한 기초자료를 제공하고자 하였다. 따라서 단면형태별로 각각 한 개씩 의 철근콘크리트 비교시험체를 포함한 4개의 장방형보와 4개의 T형보로 구성된 총 8개의 시험체를 제작하여 시공하중의 영향을 고려한 1년간 4점 가력 장기휨실험을 수행하였다. 결과로서 시간종속적인 영향을 받는 순수장기균열폭은 철근 시험체에 비해 보강근의 탄성계수가 낮은 GFRP나 AFRP-보강근 시험체에서는 2.6∼3.0배 증가하였으나 CFRP-보강근 시험체에서는 1.1∼1.4배 증가에 그쳤다. 또한 즉시균열폭을 포함한 총장기균열폭은 장방형단면과 T형단면 시험체에서 평균적으로 각각 즉시균열폭의 약 2.4와 3.1배 증가를 보여주어 보수적으로 각각 2.5와 3.5의 시간종속계수를 구분하여 제안하였다. Larger crack widths can be observed more in FRP-reinforced concrete members than in steel-reinforced concrete members as a result of the lower elastic modulus and bond strength of FRP reinforcement. The ACI 440.1R-15 design guide provides equations derived as the maximum bar spacing to control the crack widths indirectly. On the other hand, it is not concerned with long-term effects on the crack control design provisions. This study provides suggestions for how to incorporate time-dependent effects into the crack width equation. The work presented herein includes the results from 8 beams composed of four rectangular and T-shaped FRP-reinforced concrete beams tested for one year under four-point bending. Over a one year period, the crack widths increased as much as 2.6∼3.0 times in GFRP and AFRP-reinforced specimens and 1.1∼1.4 times in the CFRP-reinforced specimens compared to steel-reinforced specimens. In addition, the average multiple for crack width at one year relative to the instantaneous crack width upon the application of the sustained load was 2.4 in the specimens with a rectangular section and 3.1 in the specimens with a T-shaped section. As a result, it is recommended conservatively that the time-dependent coefficient be taken as 2.5 for the rectangular beams and 3.5 for T-beams.

FRP-보강근 콘크리트 보의 유효단면2차모멘트 재평가

최봉섭(Choi, Bong-Seob) 대한건축학회 2012 大韓建築學會論文集 : 構造系 Vol.28 No.11

The objective of this paper is to critically review equations used to calculate instantaneous deflections for FRP reinforced concrete beams. Equations for computing the deflections can be provided by ACI 440.1R-06 design guide, CEB-FIP MC-90 and Bischoff. The results obtained from test are used to assess the calculation methods suggested by the code. Although the fundamental equation (m=2) of CEB-FIP MC-90 has a good agreement comparing to ACI 440.1R-06, the existing correction factor given in CEB-FIP MC-90 are necessary to revise to more rational factors along with the type of reinforcing bar and the shape of member section.

단기하중을 받는 FRP-보강근 콘크리트 보의 휨균열폭 특성

최봉섭(Choi, Bong-Seob) 한국산학기술학회 2015 한국산학기술학회논문지 Vol.16 No.10

콘크리트 부재에서 FRP-보강근의 사용은 철근의 사용에 비해서 일반적으로 낮은 탄성계수와 부착성능으로 인하여 보다 넓은 균열폭을 초래 할 수 있다. 따라서 본 연구에서는 9개의 장방형보와 3개의 T형보로 구성된 총 12개의 시험체들 로부터 4점가력 휨실험을 통하여 얻어진 균열폭 결과들과 기존 ACI 440.1R-06 제안식으로 계산된 결과들을 비교·분석하여 설계변수들이 균열폭에 미치는 영향과 적용 범위에 대한 문제점들을 파악하였다. 결과로서 주요 설계변수의 하나인 변동 계수,  값은 0.6∼1.88 범위에서 1.05의 평균값과 약 40%의 높은 변동계수를 나타냈다. The use of FRP(Fiber-reinforced polymer) bars results in larger crack widths under service load due to the generally low elastic modulus and poor bond characteristics of FRP as compared with steel reinforcing bars. The work presented herein includes the results from 12 beams composed of nine rectangular beams and three T-beams reinforced with FRP bars tested under four-point bending. It was investigated that the bond coefficient,  in ACI 440.1R-06 equation had high variability which the coefficient of variation was 40% in the range of 0.6 to 1.88 with average 1.05.

GFRP-데크플레이트로 보강한 합성 슬래브의 휨성능 평가에 관한 실험적 연구

최봉섭(Choi, Bong-Seob) 한국산학기술학회 2009 한국산학기술학회논문지 Vol.10 No.1

본 논문은 GFRP-데크와 콘크리트를 합성한 1방향 슬래브 시스템을 제안하고자 기존의 철근트러스-데크 합성슬래브와의 비교실험을 통하여 휨성능에 대한 구조실험을 수행하였다. 실형결과 휨성능은 제안된 GFRP 합성슬래브의 시험체들이 비교시험체들 보다 우수하게 나타나, 재료의 적절한 품질관리가 이루어진다면 GFRP가 갖고 있는 내부식성의 장점을 살릴 수 있는 배기가스나 염분에 많이 노출된 건축물에 매우 효과적으로 적용할 수 있을 것으로 판단된다. In this study, the flexural experiment was conducted to propose the one-way composite slab system composed of concrete and GFRP-Deckplate by comparing with the composite deck slab system with bar-mesh. As a result of experiment, the specimens of the proposed GFRP-Deck composite slab were better than the specimens for comparison in the flexural performance. It is effective for the building structures exposed to air pollution or salt.

FRP-보강근 콘크리트 부재의 처짐 거동

최봉섭(Choi, Bong-Seob) 한국산학기술학회 2011 한국산학기술학회논문지 Vol.12 No.2

ACI 440.1R-06 설계지침에서는 FRP-보강근 콘크리트 부재의 처짐 계산을 위해 Branson에 의해 제안된 유효 단면2차모멘트를 수정·보완하여 제시하고 있다. 그러나 다수의 연구자들은 아직까지도 적용범위의 적절성에 대해 의 문점을 제기하고 있다. 이에 본 연구에서는 12개의 장방형 단면과 9개의 T형단면의 FRP-보강근 콘크리트 시험체를 제작하여 처짐 실험을 통해 얻어지는 실험값과 제안된 이론식에 의해 얻어진 계산값을 비교 분석하여 합리적인 처짐 설계를 위한 기초자료를 제안하고자 하였다. 결과로서 FRP-보강근 콘크리트 보의 처짐값은 장방형단면에서는 계산값 이 실험값 보다 과소평가 되었으나, T형단면에서는 계산값이 실험값 보다 다소 과대평가 되어 나타났다. The effective moment of inertia revising the expression proposed by Branson has been used in ACI 440.1R-06 design guide for calculating deflections of FRP-reinforced concrete members. However, its adequacy has been questioned by several researchers. The propose of this study is to provide fundamental data for the rational design of deflection by the comparison of the experimental results obtained from twelve specimens with rectangular section and nine specimens with T-shaped section to the theoretical results. As a result, it found that calculated results for specimens with rectangular section were underestimated comparing to test results, while calculated results for specimens with T-shaped section were overestimated comparing to test results.

철근콘크리트 보 처짐의 변동성 분석

최봉섭(Choi Bong-Seob) 대한건축학회 2004 大韓建築學會論文集 : 構造系 Vol.20 No.4

It is not easy to correctly predict deflections of reinforced concrete beams and one-way slabs due to the variability of<br/> parameters involved in the calculation of deflections. Monte Carlo simulation is used to assess the variability of deflections<br/> with known statistical data and probability distributions of variables. A deterministic deflection value is obtained using the<br/> layered beam model based on the finite element approach in which a finite element is divided into a number of layers over<br/> the depth. The model takes into account nonlinear effects such as cracking, creep and shrinkage. Statistical parameters were<br/> obtained from the literature. For the assessment of variability of deflections, 12 cases of one-way slabs and T-beams are<br/> designed on the basis of ultimate moment capacity. Several results of a probabilistic study are presented to indicate general<br/> trends indicated by results and demonstrate the effect of certain design parameters on the variability of deflections. From<br/> simulation results, the variability of deflections relies primarily on the ratio of applied moment to cracking moment and the<br/> corresponding reinforcement ratio.

1방향 철근콘크리트 부재의 최소두께 값에 관한 불확실성 평가

최봉섭(Choi Bong-Seob) 대한건축학회 2003 大韓建築學會論文集 : 構造系 Vol.19 No.3

Controlling deflections by the indirect method of minimum thickness is based largely on experience rather than well-documented objective measures. It is therefore necessary to develop a more rational approach to determine the appropriate span-to-depth ratios that satisfy the allowable deflection limits. Due to inherent variability of the geometric dimensions, material properties and loads, a probabilistic model is developed to assess the minimum thickness requirements for one-way members corresponding to the maximum permissible deflections specified in Design Code of Concrete Structure. Monte Carlo simulation is performed to infer probabilistic descriptions of span-to-depth ratios for reinforced concrete one-way members. The minimum thickness values given in the Design Code are investigated by the probabilistic analysis. The effects of design variables on the minimum thickness values are also shown by the results of a parametric study.